Selecting system



' Y SELECTING SYSTEM Filed Feb. 8,'1941 2 sheletsheet 1 LWP' www las 1.9

ATTORNF July 28, 1942. N. l. HALL 2,291,224

' SELECTING SYSTEM Filed Feb. v8, 1941 `2 Sheets-Sheet 2 /NVENTOR N. l,HALL A T TORNE V Patented July 28, A1942 UNITED sELEcTmG SYSTEM NathanI. Hall, Long Island City, N. Y., assigner to BellTelephone-Laboratories, Incorporated, A

New York, N. Y., a corporation of New York y Application February s,1941, serial No. 377,996

7 claims. (o1. 179-18) This invention relates to selecting and switchingsystems and particularly to systems in which selections are madeautomatically in a group of lines, trunks, or other circuits.

An object of the invention is to obtain a more uniform and more eihcientuse of the lines, circuits, or other elements comprising a group inwhich selections are made.

Another object is to obtain a preferential selection of circuits whichvaries in accordance with the-extent of their us'e.

Another object of the invention is to improve the eiiiciency ofswitching systems by obviating the selection of circuits which have noavailable outlets.

These and other objects of lthe invention are realized by means of aswitching system in which a plurality of equivalent groups of lines ortrunks are accessible to automatic switches for extending calls or otherconnections, in which the several groups are selectable under thecontrol of associated devices having varying degrees of sensitivity, andin which the selectability or preference for any particular' group oflines is varied by varying the sensitivity of the associated device inproportion to the number of calls extended to the lines of said group.More specifically the selecting system above mentioned may serve toextend subscribers lines over automatic switches to the trunks of a,plurality of groups. Any line, when calling, causes the application ofoperating voltage to a plurality of ldischarge tubes which are relatedrespectively to the several groups of trunks, the rst tube to dischargein response to the applied voltage serving to cause the extension of thecalling line to an idle trunk in the corresponding group. Since theorder in which the tubes of the group operate depends upon the relativespeed with which the ionizing current increases in their control gaps,it is possible to obtain a preferential distribution of the calls amongthe diierent trunk groups by controlling the sensitivity of said controlgaps. 'I'his desirable end is accomplished by providing an impedanceelement for each trunk group and connectgroup becomes loaded itsassociated control tubes `become less sensitive, and other tubes willdischarge first' to extend subsequent calls lto other groups of trunks.

A feature of the invention is a selecting system inwhich calling lineshave access through links to groups of trunks, in which discharge tubesrespond to calls on said lines to extend these calls over associatedlinks to the associated trunk groups, and in which the busy condition ofall telephone system to groups of links, trunks, or

other circuits. More particularly it is assumed that the subscriberslines appear on primary line switches of the well-known cross-bar typeand that these primary switches have access through links and secondaryline switches to groups of trunk circuits.

In Fig. 1 two frames of primary and secondary 'line switches areillustrated. One of these frames comprises ten primary cross-barswitches of which two, switches |00 and |0|, areill'ustrated.` Thisframe also includes ten secondary line switches of which two, switches|02 and |03, are illustrated. Ten groups of subscribers lines lol-|05appear in the vertical contacts of the ing this element in common to theelectrodes of all tubes which cause the extension of calls into saidgroup. Each call extended into a particular group causes an increasedcurrent to flow v`through the common impedance element, which in turnlowers the voltage on the control electrodes of all tubes serving thisgroup. This lowered voltage renders these tubes less .sensitivel thanthe tubes pertaining to other groups of trunks containing lighter loads.Hence as a ten corresponding primary switches,A and the vhorizontal rowsof contacts of these switches are connected by link circuits to thevertical contacts of the secondary switches on the frame. For example,the No. 0 rows of horizontal contacts of the ten lprimary switches|00-I0l are connected to the ten corresponding vertical rows in the No.`0' secondary switch |02. Similar1ythe N o. 9 rows of horizontal contactsof switches |00-I 0| are connected to the corresponding vertical rows ofcontacts of the No. 9 secondary switch |03, and the same is true of theintervening contact rows in the switches |00 and |0|.

. The ten secondary switches |02, |03 have access respectively to tengroups of trunks 06-| 01. These groups of trunks are connected to thehorizontal rows of contacts in the respective secondary switches.

Each of the ten horizontal rows of each primary switch is provided witha select magnet and a space-discharge tube. For instance, the No.horizontal row of switch |00 is provided with select magnet |08 and tube|09, and the No. 9 horizontal row of the switch is provided with selectmagnet 0 and tube |||.v As will be described more fully hereinafter, thepresence of a call on one of the subscriberslines causes the applicationof operating voltage to the control gaps of all tubes associated withthe corresponding primary switch. When the first tube discharges inresponse tol the operating voltage', thev associated select magnetoperates to select'the horizontal circuit or link for extending the callto the corresponding secondary switch. 4'I hereafter the voltage on allremaining tubes is reduced to prevent another one from discharging andcausing a double connection.

magnets and discharge tubes for each or the non; y

zontal rows. The secondary switches may have access to ten separatetrunk groups, or they may, as illustrated herein, have access to thetrunk groups |06| 01 appearing in the switches on the rst frame. Thepurpose of giving two or more frames access to the same trunk groups isto provide these vgroups with an adequate load.`

The tubes disclosed herein may be of any suitable type, such asthosehaving .envelopes filled with'argon, neon or other gases. i.

A description will now be given ofthe detailed operation of thecircuits, and for thislgpurpose reference may be had st to Fig. 2.`Assume that the subscriber of line 20|, appearing in the primary lineswitch 200, initiates a call. The re-v moval of thesubscribers receivercloses a circuit from battery through the left winding of line relay202, contacts of hold magnet 203, thence over conductor 204, through theloop 0.! the subscriber's station and returning over conductor 200through the contacts of magnet 203 and the right winding of relay 202 toground.. Relay 202 operates and closes a circuit from ground through itscontacts, conductor 200 through the winding of magnet 203, armature andback contact of'said magnet, conductor 201,resista.nce 203 to thestart'v sistor 2|4, armature and contact of relay 2|! to the negativepole of battery 2|3. The voltage thus supplied across the control gap20S- 2H is ing of magnet 203 tolground'at the contacts of relay 202.Relay 2|3 operates in this circuit, but the resistance of this relay andthe resistance of element 2 |4 is suilici'ent to preventl the holdmagnet 203 from operating at this time.

When relay 2|3 operates, it closes a circuit from the positive pole ofbattery 222, common resistor 223, contacts of relay 2 I3 to the commonconductor 224, which is connected to the start anodes 22S-226 of the tendischarge tubes 221-220 associated respectively with the ten horizontallinks 22S- 230. Each idle link in the group of ten links 229-230 ischaracterized by the presence of negative battery potential on the testconductor thereof, and busy links are characterized bythe presence ofground potential on the test conductor. For example, if link 229 isbusy, ground potential is connected through the contacts Aof a suitablerelay 23| over the sleeve conductor 232 to the start cathode 233 of theassociated tube 221. With ground potential connected to the startcathode 233 the voltage applied to the starting gap by the battery 222is insufficient to ionize the same'.

If, however, the link circuit 230 is idle at this time, an ionizingcircuit for the tube 223` may be traced from the positive pole ofbattery 222, resistor 223, contacts of relay 2|3, conductor 224,starting anode 226, starting cathode 234, test conductor 235, resistor23S, contacts of control relay 246, common resistor 241, to the negativepole of battery 231. The control gap.228234 ionizes, and insimilarfashion the control gaps of all other tubes representing idle linksionize. As soon asthe ionizing current in the control gap of some oneofthe tubes corresponding to idle links reaches sufficient value,ionization-transsufficient to ionize this gap, but the current ilowin'gis not suiilcientito operate either the magnet I 203 or the relay 2|3.Assuming that ino other line is calling at' the moment, the screen grid2| 1 of tube 2|0, which is connected in-common with the screen grids ofthe other tubes, such` 2|3, cathode 2| l, anode 220, conductor 22|,wind-f fers from the control anode to the main cathode. Assuming thatthe tube 223 the first one to reach this transfer stage, a circuit maybe traced from the'positive pole of battery 222, resistance 223,contacts of relay 2|3. conductor 224, anode 220, cathode 230, commonconductor 233, wind- .cathode 240 of tube 221 is instantly made morepositive to prevent the transfer of ionization of this tube in the eventthe link 223 hadbeen idle.

Thus the ionization of a single one of the tubes prevents the transferof ionization in all other tubes to prevent the possibility of anydouble connections.

Shortly after ionization transfers to the main cathodem of the tube mthe main anode zap discharges, and current now flows in a circuittraceable from the negative pole of battery 2 l3,

contacts axd winding of relay 2|5, cathode 233, main anode 245, windingof select magnet 24| to ground. The magnet 24| prepares the switch forthe selection of the idle link 230 and also closes a short circuitaround the resistor 2I4.

The removal of re'sistor'2l. permits sumcient current to4 flow in thecircui previously traced for the operation of the hold magnet 203.'Magnet 203 completes the connection of the line 20| to the link 23| andlocks itself in a circuit from battery 242, through the front contactand winding of said magnet, conductor 203, closed contacts of the switch200, conductor 2-33 to ground potential which in the meantime has beenconnected to this conductor in the well-known uve'potentiai of batteryIan is impressed upon the manner. The operation of magnet 203 releasesrelay 202.

After an interval following the closure of the main discharge gap oftube 228 the slow-operate relay 2|5 opens its contacts and severs thedischarge circuits of the tubes 228 and 2 I0. There upon these tubesdeionize, and the magnet 24| and relay 2|3 release. Also the relay 2|5restores its armature and recloses its normal contacts. the line 20| tothe link 230 and is held by ground potential on the sleeve conductor ofsaid link.

Preference for the diierent trunk groups to which the calling lines haveaccess is automatically varied in accordance with the load imposed Theconnection is now established fromv upon these groups by controlling thesensitivity l of the starting gaps of the tubes associated with thehorizontal links in the line switches'. The circuits for obtaining thispreferential control are disclosed more in detail inFig. 1. In thisfigure each of the ten primary line switches on each frame, such as theten switches |e|0| on the lower frame, corresponds to the switch 'Ystart cathodes H8, |42, |43, |44.y Similarly, the full negativepotential of battery |4| is impressed upon the start cathodes I9, |45,|46|41, and the same is true for the other groups of trunks. When,however, the trunk in one of these groups is taken for use, such as thetrunk |48 of the group |06, ground potential is applied to the testconductor thereof, and current now ows over a circuit traceable from thenegative pole of'battery |30, resistor |29, contacts of relay |20,conductor |20, resistor |24, conductor ||6 through the contacts ofswitch |02, conductor |40 over the busy ground connection |49 to theopposite pole of battery |30. The voltage drop in the common resistance|29 lowers the potential on the start cathodes of all other tubesserving this group of trunks |06. Therefore, when the next call appearsin vthe switch |00, and the same ls true in the other primary lineswitches, the negative potential on the-cathode ||8 of the tube |09applied to the start anode |50 from the battery ample, the No. 0horizontal link I6 of the switch |00 extends to the secondary switch|02, which has access to all ten of the trunks in the'group |06. TheNo.`9 horizontal link ||1 of the switch |03 extends to the No. 9 secondaryswitch |03,

which has access to the ten trunks of the tenth l group |01. Similarlythe eight intermediate horizontal links of the switch |00 extendrespectively to the. eight intermediate secondary switches, which inturn have access tothe eight intermediate groups of trunks. The samerelation between the horizontal links, the secondary switches and thetrunk groups existv for the second frameof switches and also for otherframes not shown.

The test conductors of the ten horizontal links |5|, is less than thevoltage impressed across the starting gaps of the other nine tubes. Forinstance, the voltage applied to the gap of tube is the sum of the fullnegative potential of battery I4| impressed upon the cathode ||9 and thefull positive potential of battery |5| impressed of the primary switch|00 appear respectively in the start cathodes ||.8||9 of the tenassociated discharge tubes |09| And the same is true of the horizontallinks of all other pri'- -mary switches. The No. 0 horizontal link ofeach No. 9 horizontal links H1, |3l, |32, |33which.

have access tothe trunk group |01 are connected through the respectiveindividual resistors |34, |35, |36, |31 to the common conductor|38,which in turn extends'through the contacts of relay |39 and the-common resistor |40 to the, negative pole of battery |4|. Likewise, theremaining cor` responding horizontal linksY are connected throughindividual resistors to common voltage supply circuits.

When all trunk groups |06|01 are idle, all test conductors are free fromground potential, and no current flows through any of the ten commonresistors |29|40. Therefore, the full negaupon the anode |52. Therefore,the tube |09 isless sensitive than the other nine tubes, and theprobability is that some one of the other nine tubes will discharge andcause the extension of the call over the corresponding into theassociated trunk group thus preventing a second call from going int'othe group |06 which already has one call.

Whenever two or more trunks in any group are in use simultaneously acorresponding heavier current flows through the common resistor |29, andthe negativepotential on the start cathodes of the associated tub'es islowered correspondingly. Thus as a-gvroup becomes more and more loadedthe tubes which cause the routing of calls into this group become lessand less responsive with the result that'subsequent calls areautomatically directed into trunk groups having lighter loads.

When all of the trunksof a group, such as group |06, become busy, achain circuit of any renders all tubes serving this group inoperative.4This condition prevails until 'some one of the well-known type may beutilized to cause the operation of the common group relay |28. Thisrelay opens the voltage supply circuit |20 and trunks in the busy groupbecomes idle, at which time the relay |28 releases to render the groupWhat is claimed is:

1. The combination in a selecting system of groups of lines,` switches,one for each group, for establishing connections with said lines,devices having dinerent degrees of sensitivity for selecting saidswitches for operation, and means for varying the sensitivity of saiddevices to vary the selectability of said switches in accordance withthe extent to which the associated line groups are used. Y

2. The combination in a selecting system of groups of' lines, switches,one for each group, for establishing connections with said lines,devices having diiierent degrees of sensitivity for selecting saidswitches for` operation, and means for vlowering the sensitivity of saiddevices to reduce the selectability of said switches in proportion tothe increased use of the associated groups of lines.

3. The combination in a selecting system of groups of lines, switchesfor establishing connections with said lines, discharge devices, one.for each of said groups, a source of voltage for 1 ber of connectionsestablished with' the corresponding group of lines.

4. The combination in a selecting system of groupsv of circuits,discharge devices, one for each group for controlling the extension ofconnections to said groups, means effective as the numberof busycircuits in any group increases for decreasing correspondingly theresponsiveness of the associated discharge device to increase the lpreference for other groups of said circuits.

6. The combination in a selecting system oi! a Vplurality of group oflines, switches having access to said lines, a plurality of groups otdischarge tubes, each group serving to cause the -extension ofconnections to a particular one oi.'

said groups of lines, a source of voltage, supply circuits, one for eachgroup o! tubes for applying voltage from said source to said tubes, andmeans for lowering the voltage applied to any particular group oi' tubesin proportion to the number of connections establishedyto the lines ofthe corresponding group. f

7. The combination in a selecting system ot a plurality of groups oflines, switches having access to s aid lirfes, a plurality ol" groups ofdischarge tubes, each group serving to Acause the extension ofconnections to a particular one of said groups of lines, a source otvoltage, supply circuits, .one for each group of tubes for applyingvoltage from said source to said tubes, means for lowering the voltageapplied to any particular group of tubes in proportion to the number otconnections established to the lines ot the corresponding group, andmeans for opening the supply circuit of any group of tubes when all ofthe lines in the associated group are busy.

NATHAN I. HALL.

